Nice!

This references a couple of OpenTherm project, so let's add the usual disclaimer:

The OpenTherm protocol is not open.

You can only find the spec for v2, they are now drafting v5. Yearly membership is about 3K if I remember correctly (without testing software, just for the spec).

There seems to be big difference in what you can do after v2, and it includes power delivery, maybe more fine grained control on heating curves and such (unclear, I don't have the spec)

Not all boilers support opentherm (but most should), and those who do don't support all features (but the most basic should always be present).